Plasma processing apparatus are used widely in the manufacturing of LSIs, LCDs, etc. The plasma processing apparatus carry out processes of etching, ashing, CVD, etc. based on the formation of plasma of reactive gases. Particularly, the dry etching technique using plasma is an indispensable fundamental technique for the manufacturing processes of LSIs, LDCs, etc.
The recent manufacturing of LSIs, LCDs, etc. uses larger silicon wafers and glass substrates, and the generation of uniform plasma in a wide area is required intensively. In regard to the dry etching technique and embedment technique for thin film formation, it is required to control plasma generation and ion energy in plasma independently.
In order to satisfy these requirements, the applicant of the present invention has already proposed a plasma processing apparatus which can generate plasma uniformly in a wide area and also can control the ion energy (refer to Japanese patent publication JP-A-He-5-144773). The proposed apparatus has the structure in which the ceiling section of the reaction chamber is airtightly sealed with a dielectric plate having the microwave transmissivity (will be termed "microwave window" hereinafter), a dielectric substance layer in which the microwave is propagated is provided above the microwave window, and a radio frequency (RF) voltage can be applied to the sample stage.
Based on the adoption of the above-mentioned structure, this apparatus can propagate the microwave flatly in the dielectric substance layer. Accordingly, by increasing the area of the dielectric substance layer and microwave window, it is readily possible to generate plasma uniformly in a large area of the reaction chamber. With the application of RF voltage to the sample stage in the reaction chamber, an electrical circuit is formed between the sample stage and the grounded section through the plasma, and a bias voltage can be generated on the sample surface. This apparatus can control the ion energy of plasma based on the bias voltage. Namely, based on the generation of plasma mainly by the microwave and the control of plasma ion energy mainly by RF voltage, it is possible to control plasma generation and plasma ion energy independently.
However, this apparatus cannot generate a stable bias voltage on the surface of a sample placed on the sample stage in some plasma processing condition, in which case the control of ion energy will be difficult. For example, the etching process for oxide films cannot be done at a satisfactory repeatability, and moreover etching does not progress or a thin film deposits on the sample in some cases.
On this account, the applicant of the present invention has proposed an apparatus which is capable of controlling the ion energy stably (refer to Japanese patent publication JP-A-He-6-104098).
FIG. 1 shows a vertical cross-section of the proposed plasma processing apparatus which is intended to perform the ion energy control stably. The apparatus is provided, on the microwave window 14 on the interior side of the reaction room 12, with a counter electrode 21 which is grounded electrically. The counter electrode 21 is a metallic plate of aluminum (Al), etc., and it has a microwave entry hole 21a for introducing the microwave into the reaction room 12.
The proposed apparatus shown in FIG. 1 is characterized to have the grounded counter electrode 21 disposed near the microwave window 14, where most of plasma is generated, to confront the sample stage 15. This electrode disposition stabilizes the plasma potential at the application of RF voltage to the sample stage 15, producing a stable bias voltage on the surface of the sample S. Consequently, it becomes possible to control the ion energy of plasma so that the surface of the sample S is exposed to ion of appropriate energy.
FIG. 2 shows a detail of portion A of the apparatus shown in FIG. 1, i.e., the side wall section of the reaction chamber. The counter electrode 21 is grounded electrically through the side wall section of the reaction chamber 11. Provided on this section are a heater 27 and another heater 31, by which the side wall of the reaction chamber 11 and the counter electrode 21 are heated to the specified temperatures.
However, in this structure of apparatus, the side wall of the reaction chamber is also grounded electrically, and therefore the side wall can possibly work as a grounded electrode for the sample stage having the application of RF voltage. On this account, the state of RF voltage application between the counter electrode and sample stage and between the side wall of reaction chamber and sample stage may vary, resulting possibly in a significant degradation of repeatability of plasma processing. For example, in the case of etching SiO.sub.2 on the surface of a silicon wafer, the distribution of etching rate across the sample surface may deteriorate abruptly.
It is important for various plasma processings to maintain the specified temperature of the inner side wall of the reaction chamber under temperature control. For example, the above-mentioned SiO.sub.2 etching uses fluorocarbon (CxFy) gas, and it is necessary to gather film formation seeds, which are created by the decomposition in plasma, to the sample surface in order to improve the selection ratio to the Si undercoat film. On this account, the sample is cooled by cooling the sample stage, while the side wall of the reaction chamber is heated to 150.degree. C. to 200.degree. C., under temperature control.
Since the apparatus of the above-mentioned arrangement is subjected to temperature control for the entire side wall of the reaction chamber, the heat produced by the control diffuses to the entire reaction chamber. Therefore, the temperature control for the inner side wall, on the other hand, is inefficient and insufficient. Moreover, the temperature control based on heating heats up the outer side (facing to the atmosphere) of the reaction chamber, making it difficult the access to the apparatus for the maintenance.